Four men serving at least 40 years for planning the failed July 21 suicide bombings in London today lost a court appeal to challenge their convictions.

Muktar Said Ibrahim, Yassin Omar, Ramzi Mohammed, and Hussain Osman were found guilty in July last year of conspiracy to murder.

They were convicted of trying to detonate rucksacks filled with explosives on three underground trains at Shepherd's Bush station, Oval station and Warren Street station, and on a bus in Hackney Road, in July 2005.

The court of appeal judeges, Sir Igor Judge, Mr Justice Forbes and Mr Justice Mackay, also dismissed applications brought by Mohammed and Osman against their sentences.

"These were merciless and extreme crimes. As they were rightly meant to be, the sentences were severe and extreme," said Judge. "Beyond doubt, however, they were utterly justified."

The attempted bombings came just two weeks after four suicide bombers attacked London's transport network, murdering 52 people.

All of the men came to Britain as refugees from countries in the war-torn Horn of Africa and were allowed to stay in the UK, or were granted British citizenship.

The attack was intended to have killed passengers and the bombers themselves, but the devices failed to go off.

The four terrorists maintained at their trial that the events of July 21 were "an elaborate hoax designed to protest against and draw attention to Britain's role in the attack upon and occupation of Iraq".

During the appeal hearing, George Carter-Stephenson QC, for Ibrahim, argued that the devices were made to look realistic "but included flaws which had been built into them to ensure that the main charge of each of those devices would not detonate".

The day after the failed attacks, police shot dead Jean Charles de Menezes, a Brazilian electrician who was mistaken for one of the bombers.

A fifth bomber - Ghanaian-born Manfo Asiedu, 34, who abandoned his part in the plot after he lost his nerve - was jailed for 33 years in November last year.

In February, five men who helped hide the July 21 bombers and provided them with false passports were jailed for terms of between seven and 17 years.